The range of motion of a joint of the body may be restricted as a result of injury. Range of motion can increase with therapy, exercise, and healing. Measurement of range of motion is important in evaluating the extent of injury and progress toward healing.
On the other hand treatment of various injuries may require temporary restriction in the range of movement, and devices such as casts, braces, elastic bandages, and corsets have been used to provide such temporary restraint. Some of these devices and some ergonomic chairs have also been used to promote a more erect posture.
Electronic sensors have been developed to measure angles between body segments and to measure range of motion of various joints, as described in commonly assigned U.S. patent application Ser. No. 08/990,912 to Arms, (“the '912 patent application”), filed on Dec. 15, 1997, and incorporated herein by reference. The '912 patent application describes a pair of housings that contain a pair of inclinometer board assemblies and the cable and plugs for their connection. The inclinometer board assemblies each include pairs of accelerometers oriented orthogonal to each other, a/d converters, a multiplexer, a voltage regulator, and a microprocessor. The microprocessor computes the angle of each inclinometer housing with respect to the other.
Commonly assigned U.S. patent application Ser. No. 09/457,493 to Arms, (“the '493 patent application”), filed on Dec. 8, 1999, and incorporated herein by reference discloses an inclinometer that includes three orthogonal accelerometers and three orthogonal magnetometers used to measure earth's gravitational and magnetic field vectors from which pitch, roll, and yaw (compass heading) are calculated. Low pass filters are provided to minimize effects due to inertial inputs to the accelerometers that might interfere with accuracy. The '493 patent application also provides a digital network to allow multiple devices to be wired together on a single bus, a feature useful for applications, such as posture monitoring.
Mechanical and electronic sensors have been developed to measure range of motion, as described in U.S. Pat. No. 4,665,928 to Linial et al. Other devices, such as those described in U.S. Pat. No. 4,958,145 to Morris, U.S. Pat. No. 5,089,808 to Amirdash, and U.S. Pat. No. 5,128,655 to Shore use measurement devices that detect whether an incline angle has been exceeded and provide an alarm when the user exceeds that prescribed angle.
Restraint on the extent of movement with the ability to perform exercises within a prescribed range is provided in U.S. Pat. No. 5,823,975 to Stark, et al. An orthopaedic restraining device is provided which provides restraint while permitting a range of exercise during rehabilitation. A communications device is included to provide feedback to the prescribing physician so the physician can evaluate the patient's progress in regard to the exercise the physician prescribed. The device is equipped to summon the patient to perform exercise with a visual alarm or a vibrator, to verify that torque used for the exercise is within a prescribed limit, to provide choices of torque and repetitions for each exercise, and otherwise give the patient immediate feedback respecting exercise. For example, the control program calculates the work or energy exerted by the patient and displays the energy exerted as a percentage of the targeted energy amount.
U.S. Pat. No. 5,593,431, to Sheldon, “the '431 patent,” determines the physical posture of a patient's body in relation to earth's gravitational field. A device with two or three DC accelerometers having sensitive axes mounted orthogonally within an implantable housing is adapted to be implanted with the sensitive axes generally aligned with the patient's body axes. The activity and body position signals from these sensors may be stored and/or used to monitor and effect the delivery of a therapy to the patient, e.g. by controlling the pacing rate of a rate responsive pacemaker. The device provides a multi-axis, solid state position and activity sensor operable along at least two orthogonal axes to distinguish the posture or positional attitude of the patient at rest and at levels of exercise.
However, the present inventors found that while the device of the '431 patent can distinguish various lying down positions from each other and from standing, the device cannot distinguish between various upright positions. For example, the device of the '431 patent cannot distinguish sitting from standing positions of the patient. Thus, a better system for monitoring is needed that provides improved ability to distinguish posture and activity in upright positions, and this solution is provided by the following patent application.